Fractionation of fatty materials



Sep. 7, 1954 R M|| ER 2,688,626

FRACTIONATION 0F FATT'Y MATERIALS Filed July 9, 1951 N5 ATTORNEY Patented Sept. 7, 1954 UNITED s Aram oFFic FRACTIGNATION F FATTY MATERIALS Application July 9, 1951, Serial No. 235,867

l0 idlaims.

This invention relates to the fractio-nation of fatty material and more particularly to the rearrangement and fractionation of fatty oils coinposed to a substantial extent of mixed triglycerides.

This application is a continuation-inpart of the prior application Ser. No, 779,645 led October 13, 1947.

Naturally occurring fatty oils, are composed to a substantial degree of mixed triglycerides. Mixed triglycerides are triglycerides made up of two or three different acyl radicals. The acyl radicals may differ with respect to chain length or with respect to unsaturation.

The properties of a fatty oil are determined by the acyl radicals which make up the component glycerides. Since the variation in the chain length of the acyl groups in most naturally occurring fatty oils is small and since small changes in the chain length of saturated acyl groups make relatively unimportant changes in the properties of the glycerides of Which they are a part, the properties of fatty oils are determined essentially by the unsaturation of the acyl radicals that form the component glycerides. The commercially important fatty oils, in most instances, contain saturated, monoethenoic and polyethenoic acyl radicals. These radicals are distributed in such a fashion that each glyceride molecule tends to be a mixed glyceride. result of this tendency, most fatty oils contain glyceride components which are not Well adapted for specific purposes even though these particular glycerides contain acyl radicals of a type which are adapted to the desired use. For example, glycerides composed of a saturated, monoethenoic and a polyethenoic acyl radical are rarely, if ever, particularly Well adapted to a specific use. A component glyceride of this sort makes a poor raw material for making soap. It cannot be used as a drying oil. It cannot be employed as such in shortenings. If the polyethenoic radical contains three double bonds, it will tend to have a poor shelf life as a salad oil. In short, such a combination of acyl radicals forms a glyceride that is ill adapted to most of the uses to which fatty oils are put. 4

Since triglycerides made up of any one of these radicals would be Well adapted to specific uses, it is obviously desirable to economically convert fatty oils composed of mixed triglycerides into more homogeneous glycerides or of segregating the relatively homogeneous triglycerides contained in a mixture of diverse glycerides. Many processes for accomplishing this have been Asa- in this sense.

(Cl. 26o-410.7)

devised and some are in large scale use. Examples of such processes are hydrogenation, Winterizing, splitting followed by fractional distillation and synthesis of glycerides from selected acid fractions, and fractionation of naturally occurring fatty oils by a selective solvent such as furfural. Each of these processes possesses some merit and each has its draw-back. Hydrogenation removes most of the polyethenoic radicals from a fatty oil. It is Well adapted for use on oils which contain a relatively small proportion of polyethenoic constituents. Winterizing and fractionation by a selective solvent such as furfural are useful insofar as they permit a fatty oil to be divided into fractions Which are made up of relatively similar triglycerides. Since many oils contain an appreciable quantity of relatively homogeneous triglycerides, by concentrating the homogeneous triglycerides into a particular fraction, products more adapted to certain uses are produced.

It is obvious, however, that glyceride frac tionation processes cannot convert mixed triglycerides into homogeneous triglycerides. To accomplish this objective it is necessary that the acyl radicals be rearranged. Splitting fatty oils,

fractionating the resulting fatty acids and then resynthesizing glycerides from fatty acids which are similar is the only method that has ever been even partly employed on a commercial scale. This method has been employed on a partial scale Certain fatty oils have been split and the resulting fatty acids fractionated. A large part of the fatty acids so obtained were sold in the fatty acid market. A minor fraction of the fatty acids were converted to relatively homogenous triglycerides which were Well adapted to certain uses. This method is so costly and the margins in this field so small that this process is practiced only on a very limited scale.

Since a process that involves splitting the triglycerides is too costly to practice, Ways have been sought to rearrange the acyl groups in glyceiides Without actually splitting oif the fatty acids. A number of methods for doing this have, in the past, been found. Since such a process involves the migration of fatty acid radicals between diiferent hydroxyl groups, it is termed interesterication. When mixed triglycerides are subjected to interesterication, it is found that the various acyl groups present are distributed amongthe available hydroxyl groups in a completely random fashion. A process which consists of rearranging the acyl groups from the even distribution that is found in naturally occurring fatty oils to a random distribution followed by fractionation increases the yield of homogeneous triglycerides over that secured by simple fractionation. By its very nature the yield of homogeneous triglycerides of such a process is limited and, hence, can be improved upon.

If it were possible to subject an oil to interesterication and simultaneously control the process in such a manner that the acyl groups present would all form homogeneous triglycerides, then no mixed triglycerides would be present in the nal mixture. This goal has not been reached as yet but one method of controlling the interesterication reaction to an appreciable extent so that it follows the desired course is known. In this process the interesterication reaction is carried out on oils which contain an appreciable percentage of saturated acyl radicals employing catalysts which are active at low temperatures. These catalysts are active at temperatures far below the melting point of the high melting point triglycerides that form. The solvent power of liquid triglycerides for solid triglycerides at temperatures considerably below the melting point of the solid triglycerides is small. When the interesterication reaction is carried out at temperatures appreciably below the melting point of the high melting point triglycerides which form, the solvent power of the liquid triglycerides present is so small that the high melting point triglycerides which form come out of the reacting mixture as a solid phase. It has been found that the acyl groups present in the solid phase no longer influence the reaction. This causes the remaining acyl groups to rearrange themselves once more until a random arrangement of those acyl groups still present in the liquid phase takes place. This causes an additional amount of high melting point solids to form. These high melting triglycerides come out of solution causing the acyl radicals to rearrange again. This process continues until high melting point triglycerides no longer come out of solution under the prevailing conditions. When this process is applied to some oils, the conversion of mixed triglycerides to homogeneous triglycerides is very materially affected. The resultant mixture may then be fractionated into products which are well adapted to certain uses. This process of guided or controlled interesterication is an elegant scientific solution to the problem when used on some oils. When the attempt is made to practice this process on a commercial scale, it is found to be too costly to permit its use.

The process is too expensive to practice on a commercial scale because of the type of active catalyst employed. The only known catalysts which are su'iciently active at moderately low temperatures are alkali metal alkoxides or their chemical equivalent. These catalysts are very active in low concentrations. But it happens that their activity is readily impaired by a a variety ofV causes. In order to keep the catalysts active they must be used in an anhydrous environment, in the absence of oxygen and carbon dioxide, and on acid-free and peroxide-free triglycerides. In order to secure a good yield of high melting point triglycerides the temperature must be sufficiently low and Sunicient time must elapse to permit the high melting point triglycerides to form and crystallize out. This means that the process requires an extended period of time.

Crude fatty oils` always contain catalyst poisons such as acidic substances, moisture, peroxides, color bodies etc. Obviously, these catalyst, poi- 4 sons must be removed and the oil dehydrated prior to adding the catalyst. This means the whole oil must be refined and preferably bleached prior to the addition of the catalyst.

After mixing the catalyst with the rened oil under conditions which insure that the catalyst is thoroughly dispersed through the oil, the mixture must now be cooled, in the substantial absence of air. Since the catalyst does notl dis- Solve in the fatty oil, it is necessary that the mixture be continuously agitated otherwise the solid fat that forms will settle and carry along the suspended catalyst particles. This would be the equivalent of removing the catalyst prior to the completion of the operation. When the reaction is completed, a slurry or semi-solid mass containing active catalyst is in the reaction vessel. The mass cannot be warmed to melt it so that it may be pumped out of the reaction vessel because this would cause the acyl groups to start to rearrange to a random distribution thus undoing the process. Hence, the catalyst must be killed prior to removing the product from the reaction vessel. If the attempt is made to use water to kill the catalyst, a soap is formed. Soap is a good emulsifying agent, so that it is not possible to rid the product of soap by Washing with water. Therefore, it is necessary to destroy the catalyst by macerating the reaction mixture with an acid and then washing the reaction product with Water to free it from the salt. After the catalyst has been killed, the mixture of triglycerides must be separated in one Way or another into fractions composed of relatively homogeneous triglycerides.

It can be seen from the foregoing that this apparently simple process in reality requires that the initial crude oil must first be thoroughly refined, then mixed with, a catalyst in the substantial absence of air, cooled with agitation for a protracted period, treated with acid without raising the temperature and then separated into fractions relatively homogeneous triglycerides.

The above prior process possesses additional draw-backs that have not been mentioned. All of the initial oil is subjected to the entire process and the process can only be employed on those oils which contain sucient saturated acyl radicals to permit a considerable percentage of solid triglycerides to form.

It is an object of this invention to convert fatty oils containing mixed triglycerides into fractions some of which will contain a higher concentration of homogeneous triglycerides than the initial oil.

It is a. further object of this invention to convert mixed triglycerides into fractions relatively concentrated with respect to homogeneous triglycerides.

A further object of this invention is to treat a mixture of mixed triglycerides and homogeneous triglycerides so that the mixed triglycerides are converted to relatively homogeneous triglycerides and the similar homogeneous triglycerides concentrated into relatively individual fractions.

An additional object of this invention is to have the fractionation or separation operation provide an especially favorable environment for the conversion of the mixed triglycerides to more homogeneous triglycerides.

An especial object of this invention is to achieve the conversion of mixed triglycerides to more homogeneous triglycerides and the segregation of the resultant triglycerides into fractions composed. of similar homogeneous triglycerides without forming any solid phases consisting of triglycerides.

A primary object of this invention is to achieve the above and other objectives of the invention economically by having each component of the process perform more than one function.

In order to more readily explain the invention, a flow-sheet of the process is shown in the single figure of the accompanying drawing.

It is to be understood that such expressions as mixed triglycerides and homogeneous triglycerides are to be considered as relative expressions. A triglyceride, none of whose acyl radicals are identical but each quite similar would be referred to as a homogeneous triglyceride when compared with, even by inference, a triglyceride, none of whose acyl radicals are identical, but whose acyl radicals differ to a greater degree than the triglyceride with which it is being compared. Since naturally occurring fatty oils contain a variety of acyl radicals and a much larger variety of triglycerides, the fractions secured by processing naturally occurring fatty oils will have materially different compositions even though each fraction will be made up of the same component glycerides. What will differ will be the percentage ofA each glyceride in the diiferent fractions. A fraction made up in large part of glycerides all of whose acyl radicals are very similar is to be regarded as a fraction consisting of homogeneous triglycerides although other triglycerides are present to a minor degree. The heterogeneity of most naturally occurring fatty oils is well established. In spite of this it is customary to designate fatty oils in terms of properties imparted by the preponderant triglycerides present so that the terminology employed herein is that which is customarily employed in this field.

This invention uses as a catalyst small percentages of alkali metal alkoxides or their chemical equivalents such as sodium methoxide in the presence of an inert hydrocarbon under especially selected conditions.

This invention also employs the selective solvent property of liquefied normally gaseous hydrocarbons, under carefully controlled conditions. The preferred solvent of the many which can be used is propane. Others that can be employed are propylene, mixtures of ethane and propane, propane and propylene, ethylene and propane, ethylene and propylene, isobutane, mixtures of isobutane and propane, butane and ethane, butane and propane, etc.

Liqueed, normally gaseous hydrocarbons such as propane under pressure not less than its vapor pressure are completely miscible with unbodied triglycerides at atmospheric temperature. When the ratio of solvent to fatty oil is four or more to one by weight the ability of the solvent to completely dissolve the fatty oil decreases at elevated temperatures. It has been found that the ability of liquefied, normally gaseous hydrocarbons to dissolve naturally occurring triglycerides varies with the unsaturation of the triglyceride. The more unsaturated the triglyceride the more rapidly does the solvent lose its ability to keep the triglyceride dissolved as the temperature is raised. In addition, certain objectionable non-glyceridic components of crude fatty oils such as color bodies which are catalyst poisons are precipitated along with the initial small amount of fatty oil that is precipitated.

Because lique'ed, normally gaseous hydrocarbons lose their ability to dissolve relatively unsaturated triglycerides more rapidly than relatively saturated triglycerides, it is possible to use these liquids as selective solvents to separate the more unsaturated naturally occurring triglycerides from the less saturated triglycerides.

The objectives of the invention are achieved by combining in a unique manner the use of the alkali metal alkoxides as active interesterication catalysts along with a selective solvent fractionation operation employing liquefied normally gaseous hydrocarbons.

The invention may be understood by referring to the accompanying flow sheet. Into an extraction tower I equipped with contacting means, such as bales, a plurality of steam coils for temperature control, liquid level controls etc. moisture-free fatty oil is pumped through line 2. Liquid propane drawn from supply tank 3 is forced by pump 4 through line 5 into the lower section of the tower in amounts controlled by valve 5. The stream of propane flowing to the tower may be heated to the desired temperature by means of a suitable heater (not shown). The temperature and pressure within thetower is controlled so that two liquid phases of different density are present. The less dense phase termed the solvent phase is made up in large part of propane. It iiows up the tower countercurrently to the more dense phase termed the oil phase. The oil phase contains only a relatively small amount of propane. Since the fatty oil contains glycerides of varying degrees of unsaturation and since propane has a preferential affinity for the more saturated glycerides, the more saturated glycerides go into the solvent phase and the less saturated glycerides concentrate in the oil phase. As the solvent travels up the tower, it contacts the oil phase which flows towards the bottom of the tower. Due to the selectivity of the propane the upfiowing solvent phase is continuously exchanging glyceride molecules with the oil phase so that the iodine value of the oil contained in the solvent phase decreases as the oil approaches the top of the tower. For this reason, the iodine value of the oil contained in the oil phase increases as the oil phase travels towards the bottom of the tower. The solvent phase leaves the tower at the top through line 6 and flows through a heater 'I and into a flash drum 8. Most of the propane contained in the solvent phase is vaporized and leaves the flash drum 8 through lines 9 and I0, a propane condenser II and is fed to supply drum 3. rIhe remaining solution of propane andv oil leaves nash drum 8 through bottom outlet line I2. The stream in line I2 branches one part flowing through line I3 to reiiux drum I4 and the other flowing through line l5 and heater IB and thence into drum I1 where most of the remaining propane is vaporized. Lines I3 and I5 are provided with valves (not shown) to control the oil ow therethrough. The propane leaves drum I1 through line I8 which, as shown, is connected to the return line I0. The nearly propane-denuded oil in drum II leaves by means of line I9 and iiows into stripping drum 20. Line I9 is provided with a suitable pressure control valve (not shown). Drum 20 is provided with a steam coil 2| and an inlet 22 for live steam. Live steam flows through the hot oil contained in drum 2B stripping it completely of propane. The steam and propane vapor pass out of drum 20 through overhead line 23. I'he propane-free oil ows out of drum through line 24 and cooler 2-5 and is passed to storage. The cooled material flowing from the cooler is one product of the process. It is a light colored, relatively low iodine value fatty oil.

The vapor mixture of steam and propane passes to any suitable condensing unit in which the steam is condensed and the propane vapors recovered. As shown, this may comprise the packed column jet condenser 26. Line 23 is connected to the lower section of the condenser and water passes through line 21 and is sprayed into the upper section of the column through a spray head. Waste water is discharged through line 28.

The propane vapors recovered from the condenser are compressed, condensed, dehydrated and returned to the propane supply drum. As shown such vapors pass through line 29 to the compressor 3e and thence through the condenser 3|. The liqueed propane is then fractionated through tower 32 which is provided with about ten trays. The overhead vapors pass through line 33 and condenser 34. The condensate flows through line 35 into a tower 36 which latter is provided with a bed of alumina. During passage through the tower any water contained in the propane is absorbed and the dehydrated propane iiows through line 31 back to the supply drum 3.

An active interesteriiication catalyst such as sodium methoxide is introduced into drum |4 through line 38. The interesterication catalyst causes the acyl groups to rearrange so that a random distribution results. The rearranged oil is pumped back into tower I from reflux drum hi through line 39 by means of pump 4|). The active catalyst dispersed in the oil accompanies the oil into the tower. In the tower the active catalyst remains in the oil phase. As it iiows down the tower it continues to cause the acyl groups to continuously rearrange. Since the down-flowing oil phase is being continuously contacted by the solvent phase coming up and since the conditions in the tower make the solvent selective, the more saturated glycerides formed as a result of the rearrangement leave the oil phase and pass into the solvent phase. The removal of the more saturated glycerides cause the remaining glycerides in the oil phase to rearrange once more since the removal of the more saturated glycerides further upsets the approach to equilibrium that the interesterication catalyst is attempting to bring about.

As the interestercation catalyst moves down the tower in the descending oil phase, part of it is poisoned or destroyed by the catalyst poisons consisting of non-glyceridic impurities contained in the charge oil. The most destructive components of this nature are the acidic materials such as free fatty acids. The oil phase, catalyst and destruction products of the catalyst leave the tower at its base through line 4|. It flows through line 4| into about the mid-point of tower 42 which is similar to tower l. Dry propane containing fatty oil is introduced by pump 43 through line 44 into the lower section of tower 42. The ratio of propane to fatty oil in tower 42 and the temperature pattern within this tower is controlled so that two immiscible liquid phases are present. The action in tower 42 is similar to that in tower I. The solvent phase flows out of tower 42 through overhead line 45. It is heated in heater 46 and flows into ash drum 41. Most of the propane contained in the solvent phase is vaporized in drum 41. Propane vapor flows out of drum 41 through lines 48 and lll, is condensed in condenser and the liqueed propane passes to the supply drum 3. The remaining oil-propane solution leaves drum 41 through line 49. Part of the solution flows through branch line 50 into reux drum 5|. The remainder passes through branch line 52 and heater 53 into flash drum 54. Lines 5|) and 5| are provided with valves (not shown) to control the quantity of oil owing therethrough. Additional propane is vaporized in drum 54 leaving through line 55 which is connected to line |0. The oil plus a small amount of dissolved propane iiows out of drum 54 through line 56 into stripping drum 51. This, like stripper 20, is fitted with an internal steam coil 58 and a nozzle for the direct injection of live steam from line 59. The remaining propane in the oil is removed in drum 51. The steam plus propane leaves drum 51 through line 60 to the condenser 26 and is subjected to the treatments previously described whereby dehydrated propane is recycled to the supply drum 3.

The oil from which the propane is stripped passes out of drum -51 through line 6| and cooler 62 to storage. This constitutes a second product of the process and comprises a high iodine fraction.

An additional amount of active interesteriflcation catalyst is pumped into reflux drum 5| through line 63. In the reiiux drum the catalyst causes the acyl groups present to rearrange into a random distribution. The oil in the reflux drum is returned to tower 42 through line 64 by means of pump E5. The catalyst contained in the oil is also added to the tower. In the tower the catalyst contained in the oil phase continuously seeks to have the acyl groups reach equilibrium and just as in tower the more saturated molecules are dissolved in the solvent phase thus preventing equilibrium from being attained and causing the rearrangement reaction to continue.

IThe oil phase plus its dissolved catalyst and catalyst destruction products leaves tower 44 through line 65 to valve controlled branch lines 61 and |58. Branch line 61 leads to pump t9 which pumps a part of the oil phase flowing out of tower 42 back into tower through line 1i) at a point between lines 2 and 5. This permits the more saturated glycerides in the oil phase leaving tower 42 to be extracted by the solvent phase in tower In this way the more saturated glycerides formed in tower 42 are transferred to tower and subsequently into the product leaving cooler 25. The more unsaturated glycerides extracted from the solvent phase by the oil phase is transferred to tower 42 and eventually leaves the system through cooler 62.

The other branch line 68 leads to pump 1| which transfers the other portion of the oil phase leaving tower 42 to tower 12. The oil phase enters tower 12 about one third of the distance down between the top and the base. Propane is charged to tower 12 through line 13 in quantities regulated by valve 14. The ratio of propane to oil in tower 12 is maintained at about 6 to '7 to 1 by weight. 'I'he temperature within this tower is controlled at but a few degrees above the temperature at which the oil and propane at the selected ratio are completely miscible. Under these conditions the propane dissolves most of the triglycerides in the oil phase but does not dissolve the color bodies, or other objectionable impurities contained in the charge oil. In addition, the interesteriiication catalyst and destruction products of the interesterification catalyst entering tower 12 are not dissolved by the propane so that the solvent phase leaving tower 4I through overhead line 14 is substantially free from substances other than propane and glycerides.

The more dense oil phase leaves tower I2 through line l5. This contains but a minor percentage of the fatty oil contained in the charge oil and the great preponderance of the non-glyceridic impurities contained in the charge oil. This oil phase flows through heater 'I6 into flash drum TI. The propane vaporized in flash drum 'I1 leaves through line 18 which is connected to the propane return line I0. The oil plus its residual propane content leaves drum TI through line 19 which transfers it through heater 80 to stripping drum 8i. Drum 8| is fitted with an internal steam coil 82 and a nozzle for the direct injection of steam from line 83. In drum 8I the remaining propane is removed through line 84 which is connected to the remainder of the propane recovery system previously described. The propane free product leaves drum 8l through line 85 and cooler 86 and is discharged from the system.

Make-up propane is fed into the system at any convenient point as, for example, through line 81 into the supply drum 3.

The volume ratio of propane to initial charge oil in a system such as described may vary from about l to 30 or more to 1. The maximum temperature in the system is at the top of tower I. The minimum temperature at the base of tower l2. It is advantageous to use the minimum ratio v of solvent to oil consistent with securing the de sired results. In general when using propane the temperature at the top of tower I will be within the range l80-195 F. when the propane/oil ratio is between about 15 to 30 to 1. The temperature at the top of tower 42 will be between about V-180 F. when the propane/oil ratio is within the indicated range. It is usually advantageous to operate the towers with a temperature gradient with the higher temperature at the top. The composition of the oil and the market to be supplied determines optimum conditions for any given plant installation. Such variables as reflux ratio, temperature pattern, propane to oil ratio, position of the oil phase interface, etc. can be varied to achieve the desired results. Since these variables are interrelated it is necessary to remember that the solvent power of propane for fatty oils diminishes as the` temperature rises if the temperature is above the 'miscibility temperature at the selected ratio.

The interrelationships of the various steps in the process can now be more readily comprehended. Since the interesterification catalyst is mixed with the oil in the reflux drums I4 and 5I in the presence of some propane the catalyst is not subjected to destructive iniiuences such as air, water and acidic materials. Air is excluded since the process operates under pressure and any air introduced with the charge oil is removed along with the propane in flash drum 8. Water. is excluded by dehydrating the charge oil and by removing any water contained in the propane in the manner described. The water contained in the propane and charge oil will not be greater than about 10 parts per million. In such quantities it is much less important than the acidic substances contained in the charge oil. A part of the substances contained in the charge oil which are catalyst poisons dissolve in the solvent phase. Since the reflux solution which flows into tower 10 I contains active interesterification catalyst and since the reflux solution contacts the rising solvent phase, the catalyst poison contained in the solvent phasereacts with the interesterification catalyst and is thereby removed from the solvent phase. In this way the interesterification catalyst performs a dual function. It directs the reaction in the desired manner and then aids in removing catalyst poisons from the succeeding oil to be rearranged. That part of the catalyst poisons in the charge oil which does not dissolve in the solvent phase, obviously, never enters reflux drum Ill. Hence, the propane possesses a third function in addition to the two previously mentioned. It aids in preventing catalyst poisons from reaching the site of the reaction. Since the equilibrium of the reaction is a random distribution and since the desired result is for the formation and separation of homogeneous glycerides in yields far removed from that secured by bringing the initial charge oil to equilibrium, it is necessary to have the rearrangement reaction take place many times and for the resultant mixture to be fractionated a multiplicity of times.

To be able to secure the desired results time must be provided. One simple method of providing this time is to size the reflux drum so that it contains sufncient volume to retain the reflux solution for at least fifteen minutes and preferably for about thirty minutes and by using an adequate reflux ratio.

Since the catalyst is introduced into the process so that it initially contacts a fraction of the charge oil which contains a greater concentration of homogeneous triglycerides than is present in the charge oil, the number of rearrangements and fractionations required is less than would. be necessary if the catalyst enters the system along with the charge oil. This advantage is secured at little or no additional capital investment.

From the foregoing it is seen that each of the steps is interrelated with and effects the action of all of the other steps. Among the functions that the propane serves are: it provides an anhydrous, oxygen free, carbon dioxide free environment; it guides the reaction; it removes catalyst poisons from the site of the reaction, and it separates one type of homogeneous triglyceride from another type of homogeneous triglyceride.

Similarly, the interesterification catalyst subserves a double function; initially it is used to rearrange the acyl radicals and then is used to remove catalyst poisons contained in the charge oil. By using reflux in the desired manner, the catalyst is used on a fraction already containing a higher concentration of homogeneous triglycerides than the charge oil, it aids in the fractionation step of the process and it provides additional reaction time.

The system described is used to continuously fractionate an initial charge oil into three fractions. One fraction discharged through cooler 25 is a relatively low iodine value fatty oil substantially free from color bodies and other objectionable non-glyceridic impurities; a second fraction discharged through cooler I52 is a relatively high iodine value fatty oil substantially free from color bodies and other objectionable non-glyceridic impurities; and a third fraction discharged through cooler 36 containingv some fatty oil, substantially all the color bodies, soap formed from the interesterification catalyst and other non-glyceridic impurities contained in the initial charge oil. Obviously, only three fractions can be produced in a three tower system when operated in the described manner. 1f pure propane were added to tower -12 and line 'i4 led to an additional propane recovery system then four products would be secured. From a theoretical standpoint every fatty oil should be converted into a number of fractions equal to one plus the number of different acyl radicals contained in the initial fatty oil. However, it is rare that it is worthwhile to split an oil into more than foul` fractions and usually three is the economic limit. This process is sufficiently ilexible to permit as close to a theoretical conversion of a given fatty oil into homogeneous triglycerides as economics dictates.

The conversion of naturally occurring triglycerides into fractions concentrated with respect to homogeneous triglycerides employing active interesterication catalysts and the selective solvent properties of liquefied, normally gaseous hydrocarbons can be carried out in other ways than the one described above.

For example, the essential advantages of the process may be achieved by splitting the overhead stream from the contact tower into two streams, one of which can be directly treated to separate and recover the solvent and oil and the other of which is contacted with the interesterication catalyst without the prior removal of solvent and returned to the tower at a point preferably below the charge oil inlet.

It will also be appreciated that it is not essential that the interesterfication catalyst enter the extraction tower. It is possible to contact a portion of the overhead stream with the catalyst, with or without the removal of solvent then separate the catalyst from the rearranged oil and return the separated oil to the tower as reuX. With some charge oils using this latter procedure savings in catalyst consumption is eiected.

Suitable catalysts for the reaction are alkali metal alkoxides such as sodium, potassium, lithium and calcium alkoxides. The alkoxide may be prepared from practically any alcohol ranging from methyl alcohol to monoglycerides. It is preferable to use a minimum of catalyst consistent with a relatively rapid reaction rate. In most instances the catalyst concentration should be between 0.05*0.5% of the oil present. Since the catalyst is a solid it is necessary that it be thoroughly dispersed throughout the oil phase. The process by its very nature maintains this condition. Although the catalysts mentioned are active, low temperature, interesterifcation catalysts, they are employed in the present invention at temperatures and conditions such that no solid glycerides can form. The temperatures in the redux drum can be easily controlled. In most instances the contents of the reflux drum will be maintained at about 180 F. since at this temperature the rearrangement reaction is rapid.

After a plant is in operation the only time water can enter the system is with the charge oil or in the propane recovery system. The charge oil can be dehydrated by heating it to 30D-350G F. and spraying it into a Vacuum chamber. The only propane that contacts water is the propane which passes through the condenser 25. Since only a few percent of the total propane circulated passes through the condenser, special precautions need be taken with only a small fraction of the propane circulated. These precautions, as explained, consist of compressing, liquefying and dehydrating the propane in units till-36. By proceeding in this manner propane containing not more than 4 5 parts per million of water is secured. This propane represents at most one tenth of the total propane circulated. This simple method of dehydrating the working fluid is responsible for one of the principal advantages of the process.

While a preferred embodiment of the invention has been described it is to be understood that this is given to explain the underlying principles involved and not as limiting the useful scope of the invention to such illustrative embodiment.

I claim:

l. A process of producing glyceridic oils which comprises initially contacting a fatty oil containing triglycerides and objectionable nonglyceridic substances in a contact zone with a sunicient volume of a liquefied, normally gaseous hydrocarbon at a temperature which insures the formation of two separable liquid phases of different density at the selected ratio; the less dense phase being comprised preponderantly of the solvent containing dissolved triglycerides, the ratio of relatively saturated triglycerides to relatively unsaturated triglycerides in such less dense phase being greater than in the initial fatty oil and the ratio of objectionable non-glyceridic substances to glyceridic substances being markedly less than in the charge oil; and the more dense phase containing the remainder of triglycerides and objectionable non-glyceridic substances of the charge oil; separating the less dense phase from the more dense phase; removing some of the hydrocarbon from the less dense phase; contacting a portion of the hydrocarbon-denuded separated less dense phase with an interesterication catalyst at a temperature sufficiently elevated and for a period of time sucient to insure some redistribution of the acyl groups of the triglycerides, returning such separated and rearranged said portion together with the interesteriiication catalyst to the initial contact zone, and recovering the oil contained in the balance of the hydrocarbon denuded separated less dense phase.

2. A process in accordance with claim 1 in which the interesterication catalyst is returned to the contact zone along with the rearranged less dense phase.

3. A process in accordance with claim l in which the charge oil is dehydrated.

4. A process in accordance with claim 1 in which the solvent is dehydrated prior to contact with the charge oil.

5. A process in accordance with claim l in which the solvent is propane.

6. A process in accordance with claim l in which the more dense phase separated from the less dense phase is contacted in a separate contact zone with additional solvent under temperature conditions at the selected ratio of oil to solvent which insures the formation of two immiscible phases of different density, the less dense phase containing the preponderant amount of the solvent and a material amount of the glyceridic components of the oil and the more dense phase containing the remainder of the solvent and glycerides and substantially all ci' the objecoil contained in the balance of the hydrocarbondenuded less dense phase.

7. A process in accordance with claim 6 in which the solvent is comprised essentially of propane.

8. A process in accordance with claim 6 in which at least a portion of the more dense phase separated in said separate contact zone is returned to the initial contact zone.

9. A process in accordance with claim 6 in which the more dense phase formed in the said second separate extraction zone is withdrawn; recycling a portion of such withdrawn more dense phase to the first said extraction zone, passing the balance of such withdrawn more dense phase to a third extraction zone; countercurrently contacting this phase in the third extraction Zone with additional solvent the temperature and the ratio of hydrocarbon to oil being selected to form two immiscible phases differing in density, said temperature being slightly above the highest temperature at which the oil and hydrocarbon are completely miscible at the selected ratio, continuously withdrawing the less dense phase and recycling it to the said second extraction zone, continuously withdrawing the more dense phase and recovering the hydrocarbon therefrom.

10. A process in accordance with claim 9 in which the hydrocarbon is propane.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,118,454 Schaafsma May 24, 1938 2,270,674 Pilat Jan. 20, 1942 2,281,865 Van Dyck May 5, 1942 2,442,539 Eckey June 1, 1948 

1. A PROCESS OF PRODUCING GLYCERIDIC OILS WHICH COMPRISES INITIALLY CONTACTING A FATTY OIL CONTAINING TRIGLYCERIDES AND OBJECTIONABLE NONGLYCERIDIC SUBSTANCES IN A CONTACT ZONE WITH A SUFFICIENT VOLUME OF A LIQUEFIED, NORMALLY GASEOUS HYDROCARBON AT A TEMPERATURE WHICH INSURES THE FORMATION OF TWO SEPARABLE LIQUID PHASES OF DIFFERENT DENSITY AT THE SELECTED RATIO; THE LESS DENSE PHASE BEING COMPRISED PREDONDERANTY OF THE SOLVENT CONTAINING DISSOLVED TRIGLYCERIDES, THE RATIO OF RELATIVELY SATURATED TRIGLYCERIDES TO RELATIVELY UNSATURATED TRIGLYCERIES IN SUCH LESS DENSE PHSASE BEING GREATER THAN IN THE INITIAL FATTY OIL AND THE RATIO OF OBJECTIONABLE NON-GLYCERIDIC SUBSTANCES TO GLYCERIDIC SUBSTANCES BEING MARKEDLY LESS THAN IN THE CHARGE OIL; AND THE MORE DENSE PHASE CONTAINING THE REMAINDER OF TRIGLYCERIDES AND OBJECTIONABLE NON-GLYCERIDIC SUBSTANCES OF THE CHARGE OIL; SEPARATING THE LESS DENSE PHASE FROM THE MORE DENSE PHASE; REMOVING SOME OF THE HYDROCARBON FROM THE LESS DENSE PHASE CONTACTING A PORTION OF THE HYDROCARBON-DENUDED SEPARATED LESS DENSE PHASE WITH AN INTERESTERIFICATION CATALYST AT A TEMPERATURE SUFFICIENTLY ELEVATED AND FOR A PERIOD OF TIME SUFFICIENT TO INSURE SOME REDISTRIBUTION OF THE ACYL GROUPS OF THE TRIGLYCERIDES, RETURNING SUCH SEPARATED AND REARRANGED SAID PORTION TOGETHER WITH THE INTERESTERIFICATION CATALYST TO THE INITIAL CONTACT ZONE, AND RECOVERING THE OIL CONTAINED IN THE BALANCE OF THE HYDROCARBON DENUDED SEPARATED LESS DENSE PHASE 